There are many situations in which an injection needle is required to be shielded after use to prevent the risk of needle stick injury. This applies not only to single use devices such as disposable syringes and the like, but also to multiple use devices such as cartridges where a disposable needle is secured, e.g. by screwing or other suitable connection action, into a cartridge or adaptor and replaced for each subsequent injection. This is especially important in clinics and hospitals where the user is injected by a clinician, where the risk of cross-infection is greater.
U.S. Pat. No. 5,476,106 discloses an arrangement in which a cannula extends diametrically through a reel mounted in housing. The reel may be rotated by means of a flat twist handle that is coplanar with the axis of the cannula and rotates about an axis in the same plane. In order to destroy the cannula after use the twist handle is twisted around its axis several times to wind the cannula around the reel and to draw it into the housing.
A problem with this arrangement is that it encourages two-handed use by the user holding the medical instrument in one hand and twisting the twist handle by several revolutions with the other. When grabbing the twist handle, the user is likely to approach it from the front or side, thus increasing the risk of inadvertent needle stick injury. Also, the user will need to grip and release the twist handle several times when retracting the cannula and thus increases the likelihood of an accidental needle stick injury. The manual winding of the lever to retract the needle to a safe position takes some time. Manual effort and dexterity on the part of the user is necessary which might be particularly difficult for people with limited strength and/or movement.
Embodiments of the invention seek to provide retractable needle assemblies which overcome some or all of these problems.